1. Field
One embodiment of the present invention relates to a stamper for a discrete track recording (DTR) type magnetic recording media, a method of manufacturing a DTR type magnetic recording media using the same, and a method of manufacturing a stamper for a DTR type magnetic recording media.
2. Description of the Related Art
As a media for realizing high capacity recording, many developments of discrete track recording type magnetic recording media have done. Patterns of the DTR type magnetic recording media are largely divided into patterns of data area and patterns of servo areas.
The data area includes a recording track portion. The recording track portion is to form a user recording area for recording and reproducing user data by a head, and has patterns in which toric magnetic tracks are arranged at a specified cycle (track pitch Tp) via nonmagnetic guard bands. The magnetic track is formed of a ferromagnetic material, for example, CoCrPt. The nonmagnetic guard band is an unrecordable area, and separates a data recording layer radially. Further, the toric magnetic track is divided into sectors in the circumferential direction by the servo areas, and formed so that a radial width Tw of the magnetic track is larger than that of the nonmagnetic guard band.
The servo areas are prebit areas in which patterns of magnetic material/nonmagnetic material corresponding to information necessary for positioning the head are formed. The shape of the servo areas is a circular arc to be the orbital of access of the head to a magnetic recording apparatus, and is formed such that the circumferential length thereof becomes long in proportion to the radial position.
The servo areas are generally comprising a preamble portion, an address portion, and a deviation detection burst portion (hereinafter, burst portion), and the servo areas are formed into patterns of magnetic material/nonmagnetic material in the same manner as the data area.
The occupancy rate of magnetic material factor varies in the data area and the servo areas.
An ultrafine structure of such a DTR media with the track pitch of 400 nm or less cannot be manufactured by a method using photolithography. Meanwhile, a method of manufacturing patterns on an entire disk surface by electron beam lithography or the like leads to low mass productivity. The DTR media having such an ultrafine and large-area structure is manufactured by, for example, an imprint method. The imprint method, to be described in more details later, is a method in which a resist film is applied onto a recording layer formed on a substrate, a stamper having patterns with protrusions and recesses inverted with respect to patterns to be formed is pressed onto the resist film to transfer the patterns to the resist, and a magnetic film is processed according to the patterns.
A UV type imprint method and a hot embossing type imprint method have been known as the imprint method. The UV type imprint method is suitable for forming ultrafine and highly precise patterns. On the other hand, the hot embossing type imprint method is suitable for forming complicated shapes and high-aspect structures. However, the two methods have had the problem of their low throughput.
Examples of the imprint method for improving throughput include a high pressure type imprint method in which high pressure is applied to between a substrate and a stamper at room temperature to offset film thickness unevenness.
A stamper for a magnetic recording media to be used in the general imprint method can be manufactured by use of the electron beam lithography, X-ray lithography and the like, and for example, a master disk can be also reproduced by use of the imprint method. Jpn. Pat. Appln. KOKAI Publication No. 2005-38477 discloses a method of manufacturing a stamper by use of the imprint method.
A stamper for a magnetic recording media has recesses corresponding to magnetic portions after completion of the media. By using stampers of different areas of the bases of the recesses corresponding to respective magnetic portions after completion of the media, the above-described DTR type magnetic recording media having patterns with different occupancy rate of magnetic material can be manufactured.
Herein, in the case where a normal stamper in which the depths of recesses are equal is used in the manufacture of magnetic recording media, the spatial volumes of recesses vary with the respective areas of the base. The resist volume necessary for filling the space varies between areas of small spatial volume and areas of large spatial volume. The difference in necessary resist volume is compensated in such a manner that the resist existing around the areas of large spatial volume moves to the spaces of the recesses in the area. As a result, there occurs unevenness in the movement amounts of resists depending on pattern areas, and the film thickness of resist residues in patterns transferred by recesses of large area of the base becomes thinner than that of resist residues in patterns transferred by recesses of small area of the base.
When unevenness occurs in the film thickness of resist residues, a problem arises in removing residues by reactive ion etching (RIE) of oxygen or the like. That is the problem that resist residues of thin film thickness are removed before resist residues of thick film thickness are removed, and accordingly, side etching is performed excessively on the portions where the resist residues have been removed first.
Patterns of protrusions and recesses transferred by use of a stamper broaden due to RIE for use in removing resist residues, Ar iron milling for use in processing a magnetic film, and the like. In the broadening, there occurs unevenness according to respective pattern areas if the above-described excessive side etching occurs. For this reason, there occurs a difference in broadening of patterns depending on pattern areas between a stamper pattern as a design value and the pattern after completion of media. As a result, it becomes difficult to design a stamper for manufacturing DTR type magnetic recording media of desired dimensions. The problem arising from the difference in resist movement amount does not happen in the UV type or hot embossing type imprint method, and it is the problem peculiar to the high pressure type imprint method.
Jpn. Pat. Appln. KOKAI Publication No. 2005-38477 discloses a stamper for transferring patterns of protrusions and recesses to a data recording area, but there is description that the above “data recording area” does not include an area where servo patterns for tracking are recorded (servo area), a retreat area of a magnetic head, or the like. In other words, the stamper of the Jpn. Pat. Appln. KOKAI Publication No. 2005-38477 does not take into consideration transferring patterns to areas of different occupancy rate of magnetic material.
J. Vac. Sci. Tecnol. B21 (1), January/February 2003 describes that, when aspect ratios are varied between patterns in nano imprint, the amount of moving resists changes together with aspect ratios, and the depth at which resists are filled in recesses of the stamper also changes. The literature describes that adjustment is made by changing resist viscosity and imprint time. In the literature, a stamper of constant depth of recesses is employed.